Circuit arrangement for producing two frequency independent mutually phase shifted output a.c. voltages from two input a.c. voltages

ABSTRACT

A circuit arrangement wherein two output a.c. voltages having a mutual phase shift are derived from two input a.c. voltages. The mutually phase shifted output voltages are frequency independent and two phase shifting units included in the circuit are comprised of resistances and of reactances of the same kind, one of the phase shift units including a series connected reactance, and two resistances having a tap therebetween forming one terminal of one of the output voltages, and the other phase shift unit including a series connected resistance and two reactances having a tap therebetween forming one terminal of the other output voltage. The second terminal of both output voltages is constituted by interconnected taps on voltage dividers connected to the two input voltages.

United States Pa-tent v 1191 J Narayan 1 11- r 3,775,668 Nov. 27, 1973 CIRCUIT ARRANGEMENT FOR PRODUCING TWO FREQUENCY INDEPENDENT MUTUALLY PHASE SHIFTED OUTPUT A.C. VOLTAGES FROM TWO INPUT A.C. VOLTAGES [75] Inventor: Venkat Chellam Narayan, Spreitcnback, Switzerland [7 l5] Assignee: Aktiengesellschaft Brown, Boveri 8:

Cie, Baden, Switzerland 22 Filed: June12, 1972 211 Appl.'No.: 261,932

30 Foreign; Application'Priority Data June 15, l9 7l Switzerland....'..1 8687/71 521 u. s.c1.... 323/122 323/126 1511 1111. C1. 110311 7/18, H03h 7/50 [58] Field ofSea rch 307/262; 323/ 08, 323/109, 110, 111, 112, 120, 121, 122, 123,

[56] References Cited UNITED STATES PATENTS 1 2,997,236 8/1961 Hammer" ..323/125x 2,968,759 l/l961 McKenney etal ..323/122x 3,213,291 10/1965- Reid...;....; 323/123 X 3,544,886 12/1970 1166 et a1. 323/123 x FOREIGN PATENTS OR APPLICATIONS 605,259 7/1948 Great 131113111 .3 323/124 Primary Examiner-A. D. Pellinen Attorney-Ralph E. Parker et al.

[57] ABSTRACT A circuit arrangement wherein two output a.c. voltages having a mutual phase shift are derived from two input a.c. voltages. The mutually phase shifted output voltages are frequency independent and two phase shifting units included in the circuit are comprised of 8 Claims, 2 Drawing Figures g 8 P I 11 1 1 U U 2 1' i 4 0 1 T l ll 12 z 7- 1l U 1 T2 O M CIRCUIT ARRANGEMENT.EonrRonuCrNo rrwo FREQUENCY INDEPENDENT 'MUTUAKILLY EPHASE SHIFTEDOUTPUT A.C. NOLTAGESEFROM TWO INPUT A.C.-YOLTAGES The present invention relates .to a circuit arrangement with phase-shift elements, by meansof which, from two. input-a.c. voltages, twooutputatc. :vo-ltages can'beproduced whichchave afrequency-in'dependent mutual phaseshift.

In line protection techniques, frequently two a.c. voltages-or currents are employed to -detectand ;.pin-

pointa short-circuit. In this field-in particular, it'risffrequently necessary toprovide oneofthetWoaIternating quantities with an additional phase shift --vis-a-'vis the other, .in order to achieve an'optimum lprotective action.

. g i ln accordance with *a :pr'eferretl embodiment of the invention, :the first phaseeshiftsunit a containsaa resistor andatwo-capacitors, and*'the'- secon'd-.=unita capacitorand two resistors. 1

*ln 1 a further enibodiment, rathe :ra'tio i' between the tea- =pacitances ofthe twozcapacitors intheifirstphase-shift unit; is variable. This?likewiseenablestherphase shift .to

be varied.

-As an 'altemative to thie -foregoing; or =in. combination with it, the ratio between"therresistancesdfithe 'twoiresistorsain th'e second;phasesshift unitman -be:made variln.known-circuits, one of the measuring circuits con- I tainsrphase-shift elements in the "form "of resistors, ca-

pacitors or chokes.- For example in -Brown 'Boveri'Mitare connected and in order to reduce the frequencydependence, these impedances arranged to behave at the nominal frequency as conjugate complex impedances (see for example Austrian Pat. specification No.

Conjugate complex impedances, however, consist .in the simplest case of resistor and capacitor on the one hand and resistor and inductor on the other.

'The drawback is that these circuits only provide an adequately frequency-independent phase shift within a narrow frequency range.

The object of the invention is to provide a circuit of the kind introductorily describedw-hich'makes it possible to use impedances of the same kind, and which-is distinguished by simple design and a very large degree of independence of frequency.

In accordance with the invention, this object is achieved in that one of the input a.c. voltages is applied to a first divider circuit and a first phase-shift unit; in that the other of the input a.c. voltages is applied to a second divider circuit and asecond phase shift unit; in that the tappingpoints of the divider circuits are connected to one another and to an output terminal common to the output a.c. voltages; in that the first and sec fc'o'ntai'n :a transformer "with -a napping. This able.

-i'lf'the dividercircuits:in're'aehcaseconsist'of tworesistors, then this econstitutes a simple I design.

Advantageously,ithedividercircuits'willi each-case "rovides conversion of highririputtazc. voltages to suitalilerlower values, .;or vice-'versa.

ZFlG. 1 is =a-schematic .of a laphase shifter embodying the *:principles.=of' theinvention, and I FIG. 2 is a vector diagram illustrating the .principles 'ofithe invention. I

As shown in 51 16. 21 ean input am. voltage U :isaapplied lfrom transformeriT .in #pa'ra llel ito adivider circuit, .con-

sisting f :two series-connected resistors T and T Y and to a gphase-"shift' unitf' l he firstphase-shift unitrcontains, :in series, :a rlesistor R1 and two :capacitors C, and

"C' ',,."Between.- the ju nction of these capacitors and the junction of' t'he resistors T T .a first output :a:c. volt- The other input .aic. voltageU is likewise applied from transformer I; to series-connected. resistors T 1,

0nd phase shift units consist of resistances and of reactances of the samekind; in that in the first phase shift unit the reactance is divided, so that between the divi- "sion and the output terminal a first output a.c. voltage can be picked off; and in that in the second phase shift unit the resistance is divided, so that between the division and the output terminal a second output a.c. voltage can be picked off. I

lt is advisable to design the phase-shift units in such va'fashion that the ratio of resistance to reactance 'is variable. ln this fashion, the phase shift between the output a.c. voltages can be varied.

T and a second phase-shift unit. This latter contains, in series, a capacitor C .and two resistors -R' .;and -R'/ Between the junc'tionof Jt'hese resistor-sand the junction aofmhe-resistors'T 'T .a second output a.c. voltage U can be picked :off.

"The mapping points of the divider circuits are. taken commonly to an output terminal Mbecauseit he output a.c. voltages and U- are related to -'a common reference potential. The terrn ftappi'ng points is not meant to indicate that the input ac. voltages are :in :each case split equally. v

By means of the .divider circuits, the input a.c. voltages are simply halved in this example, and this has been indicated by U 12 and'U,/2. The other voltage drops .are indicated by the indices of the particular components.

The principle of the phase shi-ftcircuit in-accordance with the invention, is illustrated in .EIG. 12.

The designations of the voltagesas well as their reference directions, are. evident from FIG. 1.

" hand and U on the other, there is a phase difference .of 90 so that one can-make use of the fiangle in a semicircle" construction. The-top semicircle,-struck The conditions are similar in the case of the second phase-shift unit.

Simply in order to better illustrate the relationships involved, U U i/2) U /2) is aligned in the same direction as U assumed to be equal in magnitude, and has been drawn in the same figure.

U likewise lags U and U by 90"and the geometric sum is U The corner A, with rising radian frequency, traverses an infinite number of possible points along the bottom semicircle, in the clockwise sense.

Between the output a.c. voltages U'j and Ugthere is a phase shift a and this can be adjusted in the manner hereinb 'efore described. It'will be assumed therefore, purely by way of example, that the ratio of the resistances of resistors R and R" is altered. This results in a change in the direction of U so that if U, stays unchanged, the phase shift a varies.

The essential thing, however, is that this phase shift is virtually frequency-independent; at a 90, in fact, it is entirely frequency-independent.

By way of explanation, let one consider anincrease in the radian frequency w by an amount such that the original corners A, B, have displaced to A and B. The

configuration of the voltage vectors which then results,

has been omitted simply in order not to overburden the illustration. However, it will be clear that U, and U will change their directions in the same direction of rotation so that their mutual phase shift remains practically unchanged.

In FIG. 2, aphase shift a of 90 has been shown. This is a value which is frequently required and furthermore has the advantage that it is completely independent of frequency. i

In accordance with FIG. 2,'U and U havebeen illustrated with the same magnitude and phase,although.of course this has been done purely for the sake of simplicity. If, for example, one is concerned with two of the phase voltages of a three-phase system, then of course the actual'phase shift between U, and U' is 120 +11, or being determined by the circuit arrangement in accordance with the invention and being adjustable between and 180.

If, instead of the capacitors shown in FIG. 1, inductors are used, the principle remains unchanged.

Although the input a.c. voltages have been shown halved in the drawing, this is by no means a condition. In fact, arbitrary division factors are possible.

If it is input alternating currents which are involved, then these can very easily be converted into input a.c.

-voltages, across a reistor.

[claim 1 1. In a circuit arrangement for producing two output a.c. voltages having a mutual phase shift at least approximately independent of frequency from two input a.c. voltages, the combination comprising a first voltage divider and a first phase shift unit to which one of said input a.c. voltages is applied, a second voltage divider and a second phase shift unit to 'which the other input a.c. voltageis applied, respective tapping points on said first and second voltage dividers connected to each other and to an output terminal cornmon to both of the output a.c. voltages to beproduced, said first and second phase shift units each consisting of resistances and of reactances of the same'kind, means providing a first tap between reactances of said first phase shift unit to establish one" of said output a.c. voltages b'etween saidfir'st tap and said common output terminal,- and the resistanceqeactance ratio of each unit is variable.

, 3. A circuit arrangement as defined in claim 1 for providing twofrequency independent output a.c. voltages mutually shifted in phase wherein said first phase shift unit includes a resistor and two capacitors between which said first tap is made, and wherein said second phase shift unit includes a capacitorand two resistances between which said second tap is made, said resistances and capacitors of said first and second phase shift units being respectively connected in series.

4. A circuit arrangement as defined in claim 3 for providing two frequency independent output a.c. voltages wherein the ratio of the capacitances of the two I capacitors of said first phase shift unit is adjustable.

voltages.

5. Acircuit arrangement as defined in claim 3 for providing two frequency independent output a.c. voltages wherein the ratio of the resistances of the two resistors of said second phase shift unit is adjustable.

6. A circuit arrangement as defined in ,claim ,1 for providing two frequency independent output a.c. voltages wherein said first and second voltage dividers are each constituted by resistors connected in series and between which said tapping points are made.

7. A circuit arrangement as defined in claim 1 for providing two frequency independentoutput a.c. voltages wherein said first and second voltage dividers each include a transformer having taps on the windings thereof.

8. In a circuit arrangement for producing two output a.c. voltages having a mutual phase shift at least approximately independent of frequency from two input I a.c. voltages, the combination comprising a first voltage divider and a first phase shift unit to which one of said input a.c. voltages is applied, a second voltage divider and a second phase shift unit to which the other input a.c. voltage is applied, respective tapping points on said first and second voltage dividers connected to each other and to an output terminal common to both of the output a.c. voltages to be produced, said first and second phase shift units each consisting of resistances and reactances of the same kind, means providing a first tap between reactances of said first phase shift unit to establish one of said output a.c. voltages between said first tap and said common output terminal, and means providing a second tap between the resistances of said second phase unit to establish the other output a.c. voltage between said second tap and said common output terminal, said reactances of said first phase shift unit and said resistances of said second phase shift unit being divided by said first and second tapping respec-.

tively in such a ratio as to produce a phase shift of substantially between said first and second output a.c. 

1. In a circuit arrangement for producing two output a.c. voltages having a mutual phase shift at least approximately independent of frequency from two input a.c. voltages, the combination comprising a first voltage divider and a first phase shift unit to which one of said input a.c. voltages is applied, a second voltage divider and a second phase shift unit to which the other input a.c. voltage is applied, respective tapping points on said first and second voltage dividers connected to each other and to an output terminal common to both of the output a.c. voltages to be produced, said first and second phase shift units each consisting of resistances and of reactances of the same kind, means providing a first tap betWeen reactances of said first phase shift unit to establish one of said output a.c. voltages between said first tap and said common output terminal, and means providing a second tap between the resistances of said second phase shift unit to establish the other output a.c. voltage between said second tap and said common output terminal.
 2. A circuit arrangement as defined in claim 1 for providing two frequency independent output a.c. voltages mutually shifted in phase wherein said first and second phase shift units are of such construction that the resistance-reactance ratio of each unit is variable.
 3. A circuit arrangement as defined in claim 1 for providing two frequency independent output a.c. voltages mutually shifted in phase wherein said first phase shift unit includes a resistor and two capacitors between which said first tap is made, and wherein said second phase shift unit includes a capacitor and two resistances between which said second tap is made, said resistances and capacitors of said first and second phase shift units being respectively connected in series.
 4. A circuit arrangement as defined in claim 3 for providing two frequency independent output a.c. voltages wherein the ratio of the capacitances of the two capacitors of said first phase shift unit is adjustable.
 5. A circuit arrangement as defined in claim 3 for providing two frequency independent output a.c. voltages wherein the ratio of the resistances of the two resistors of said second phase shift unit is adjustable.
 6. A circuit arrangement as defined in claim 1 for providing two frequency independent output a.c. voltages wherein said first and second voltage dividers are each constituted by resistors connected in series and between which said tapping points are made.
 7. A circuit arrangement as defined in claim 1 for providing two frequency independent output a.c. voltages wherein said first and second voltage dividers each include a transformer having taps on the windings thereof.
 8. In a circuit arrangement for producing two output a.c. voltages having a mutual phase shift at least approximately independent of frequency from two input a.c. voltages, the combination comprising a first voltage divider and a first phase shift unit to which one of said input a.c. voltages is applied, a second voltage divider and a second phase shift unit to which the other input a.c. voltage is applied, respective tapping points on said first and second voltage dividers connected to each other and to an output terminal common to both of the output a.c. voltages to be produced, said first and second phase shift units each consisting of resistances and reactances of the same kind, means providing a first tap between reactances of said first phase shift unit to establish one of said output a.c. voltages between said first tap and said common output terminal, and means providing a second tap between the resistances of said second phase unit to establish the other output a.c. voltage between said second tap and said common output terminal, said reactances of said first phase shift unit and said resistances of said second phase shift unit being divided by said first and second tapping respectively in such a ratio as to produce a phase shift of substantially 90* between said first and second output a.c. voltages. 